Materials Science Forum Vols. 532-533

Abstract: The pressure infiltration process of porous preforms by molten metals was investigated numerically in this paper. The finite element model of heat and mass transfer of the infiltration in liquid infiltration extrusion process was founded by the introduction of a new continuum model of fluid in porous medium and a distribution resistance concept. The proposed model can describe the transient flow behavior of semisolid materials qualitatively. Numerical simulations were developed in particular for non-isothermal infiltrations which take into account the thermal aspects (the mould, the fibres and the metal are initially preheated at different temperatures). The temperature distribution, infiltration front and infiltration depth in the infiltration area were gained by the simulation of ANSYS／FLOTRAN code. It is shown that the fiber volume fraction and initial temperature have a strong effect on the infiltration process. The simulation results of axisymmetric infiltration have a good agreement with their experimental ones. In addition, the infiltration time was predicted to get the effective infiltration depth based on the simulation results.

Abstract: The associated modeling method of complex foundry system was investigated under software environment of PRO/E and ANSYS. The 3D-structure of K4169 superalloy shell castings constructed by applying PRO/E was guided into ANSYS to reconstruct the whole foundry system. The variation of temperature field with solidifying time was calculated by ANSYS to check each key node in casting structures. According to the temperature changing curves of key nodes, the grain structural feature values were obtained by using consecutive nucleation model. Based on the 2D cellular automaton method, the evolution of grain structure in some sections of casting was visually simulated. The results of simulation are good accordance with the measured grain feature values.

Abstract: Based on an presented adaptive-surface elastic-plastic asperity contact model which can greatly decrease contact computing time and keep the precision loss less than 5%, a series of 2-D rough surface profiles with different roughness and correlative length are numerically generated to investigate how to select the threshold used in this model for different adaptive rough surfaces. The results show that well acceptable precision of the elastic-plastic contact calculation would be derived when the ratio of threshold to root mean square curvature, δ 1.0 10 6mm2 − < × .

Abstract: This research presents a new modus of electrochemical finishing as a finish process using an effective design of forming sheet electrode on zinc alloys beyond traditional process of die casting on the surface of castings instead of the conventional hand or machines polishing. In the current experiment, the author takes an outer shell of toy vehicle for instance; five types of design electrode are used and supplied with continuous direct current in the experiment of electrochemical finishing. For the design electrodes, a thin plate with small end radius and small wedge angle are associated with higher current density and provides larger discharge space and better polishing effect. The electrode with spherical head performs the best. The electrochemical finishing after die casting saves the need of hand or machines polishing just needs quite short time to make the surface of castings smoothing and bright. An effective and low-cost polishing of the surface of castings is presented.

Abstract: This paper reports two investigations on the edge chipping in rotary ultrasonic machining using finite element analysis (FEA). The first FEA investigation establishes a relationship between edge chipping thickness and cutting force. The second FEA investigation is to understand the effects of three parameters (cutting depth, support length, and pre-tightening load) on edge chipping thickness. The investigation results showed that the edge chipping thickness could be reduced by increasing support length and decreasing cutting force.

Abstract: In this paper, the effect of strain rate has been considered in the simulation of forming process with a simple form combined into the material law. Quite a few researchers have proposed various hardening laws and strain rate functions to describe the material tensile curve. In this study, the strain rate model Cowper-Symonds is used with anisotropic elasto-plastic material law in the simulation process. The strain path evolution of certain elements, when the strain rate is considered and not, is compared. Two sheet materials, Cold-reduced Carbon Steel (SPCC) JIS G3141 and Aluminum alloy 6112 are used in this study. Two yield criteria, Hill 48 and Hill 90, are applied respectively to improve the accuracy of simulation result. They show different performance when strain rate effect is considered. Strain path of the elements in the fracture risk area of SPCC (JIS G3141) varies much when the strain rate material law is used. There is only little difference of the strain distribution of Al 6112 when the strain rate effect is included and excluded in the material law. The simulation results of material SPCC under two conditions indicate that the strain rate should be considered if the material is the rate-sensitive material, which provides more accurate simulation results.

Abstract: This paper aims to study the effect of stress relieving on Limit Dome Height (LDH) of Ti-TWBs at elevated temperatures. This is achieved by developing a newly constructed heating system. The elevated temperature of the system can be varied and monitored by a separately control panel. All Ti-TWBs were prepared and used to examine the LDHs under elevated temperatures. Selected specimens were heat-treated at 600°C within an hour before being formed by HILLE machine. Meanwhile, the temperature of tool heating system was also adjusted from room temperature to 550°C. Specified tests were carried out to examine the stress relieving effects of Ti-TWBs on the LDHs with the temperature control panel. In addition, investigations were carried out to ascertain whether the elevated temperatures of the critical tooling components, i.e. the die and the blank holder, could result in any significant effects on LDHs of Ti-TWBs. The findings show that LDHs of Ti-TWBs can be improved by stress relieving. The stress relieving condition can be obtained by nearly isothermal forming of specimens at a range of 550°C to 600°C.

Abstract: Strong interest in producing ultra-light-weight, high corrosion-resistant, heat-proof and tougher advanced products has prompted potential development of titanium tailor-welded blanks (Ti-TWBs) to construct the critical parts of structures and panels in automotive applications and some other advanced industries. However, the capability to predict the forming behavior of the stamped TWBs without failure lags far behind the manufacturing technology. It is proven that the ductility for most of the titanium alloy sheets can be significantly improved at elevated temperatures. Nevertheless, such study of stress-strain behavior on the weldment of Ti-TWBs has not been fully investigated. This paper aims to analyze the forming behavior of the Ti-TWBs at different elevated temperatures using a finite element analysis. The distinctive mechanical properties of the base metals and weldment for the forming simulations will be acquired experimentally. Finally, it is found that, due to the increase of ductility, the forming behavior of Ti-TWBs will not be considerably improved unless the forming temperature is kept between 500oC and 600oC.

Abstract: This paper presents a decision model that applies the Superiority and Inferiority Ranking (SIR) method in identifying the best material option. It has the strength to handle imprecise information, in different units of analysis, for the evaluation process that ranks the material options in preference order. It is demonstrated with an example of selecting materials for a pump.

Abstract: This paper presents a multi-spectrum analysis method for the characterization of the surface generation in single-point turning of brittle single crystals. The features on the diamond turned surfaces were extracted and analysed by the power spectrum analysis of the surface roughness profiles measured at a number radial sections of the workpiece. By the analysis of the variation of the spectral patterns in the multi-spectrum plots, the surface roughness and materials effect on surface generation are found to be strongly related to the power spectrum. This provides an important means to explain quantitatively the effect of factors affecting the surface generation in diamond turning brittle crystals.